Human Genome Project
The Human Genome Project was started in 1990 as an international effort that had two purposes. The first was to map the location of genes in the human genome. The second was to find the sequence (order) of nucleotides (adenine - A, guanine - G, cytosine - C, or thymine - T) (called bases) that make up the DNA of the human genome. The bases are repeated millions or billions of times throughout a genome. The human genome has three billion pairs of bases. The particular order of the bases is very important. The order determines whether an organism is human, or another species of plant or animal, or indeed bacteria or fungi, etc.
A working draft of the genome was announced in June 2000 and the majority of the sequence was finished in April 2003. The next challenge will be to determine the function of all the estimated 30,000 human genes and apply this information to human biology. The genomes of many other organisms have also been sequenced and many more are in progress. The list includes the yeast Saccharomyces cerevisae, the roundworm Caenorhabditis elegans, the fruit fly Drosophila melanogaster, the plant Arabidopsis thaliana, the mouse Mus musculus, the rat Rattus norvegicus and the mosquito Anopheles gambiae, as well as many other bacteria, fungi and viruses.
How was the genome sequenced?
The sequencing of the human genome involves figuring out the order of all three billion bases that make up the DNA. This was one of the major challenges of the Human Genome Project. The process, which was automated for the project, includes several steps:
- The chromosomes are broken into shorter pieces of DNA.
- Each single-strand short piece is used as a template for the enzyme DNA polymerase to make a new, complementary piece of DNA. The polymerase can add one of two types of bases to make the new piece of DNA. It can add a normal base (A, G, C, or T) or it can add a version of one of these bases that stops replication because the modified base cannot have another base added after it. The right concentration of these bases along with normal bases will result in many different strands of DNA being made, each a different length.
- The next step is to separate the newly made strands by gel electrophoresis based on their size. Shorter strands travel faster through the gel than longer strands. If the second step was successful, an original strand that was 10 bases long will result in 10 different strands separated out by size on the gel, each one base longer than the next.
- The base that is at the end of each strand has a fluorescent tag attached, a different colour for each of the bases. These colours can be seen with a fluorescent microscope and the sequence of the DNA is determined by the sequence of colours that come up on the gel. For example, a sequence of bands that are red, green, green and blue might mean that the four-base strand was made up of adenine, guanine, guanine and cytosine (AGGC).
- A computer reads the colours and determines the sequence, which it then combines with all of the other sequences to eventually make up the whole genome. This sequence information is then submitted to large public databases so that other researchers can use it and add to it.
These human genome sequences do not represent any one person's genome. They are intended as a starting point for broad comparisons across humanity. The knowledge can be applied to everyone because all humans share the same basic set of genes as well as the development and maintenance of their biological structures and processes.
Applications of the Human Genome Project
The current and potential applications of the Human Genome Project are numerous. With the sequence of the majority of human genes now established, recent work has been focussed on the function of genes and how changes in the sequence relate to health and disease. The description of the genome has led to interest in other "omes" such as the proteome and the metabolome. As we find out more about human genes and how they work, we may be able to develop new ways to diagnose and treat more diseases.
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